The present invention relates to multiple hydrocyclone apparatus.
In the paper-making industry, and in related industries, hydrocyclones are used for removing contaminants from liquids. For example, paper stock consisting of a suspension of cellulose fibers in water is ordinarily cleaned before it is fed to a paper-making machine. As is well known to those skilled in the art, a hydrocyclone is a device having a hollow body, an inlet to the interior of the body and two outlets from the interior of the body. The interior of the hydrocyclone body is configured so that stock entering through the inlet flows in a swirling pattern within the body and centrifugal forces within the swirling flow segregate various portions of the stock according to their relative densities. The lighter fraction exits from the hydrocyclone through one of the outlets and the heavier fraction through the other. Thus, if the contaminants to be separated from the stock are of lower density than the stock itself, the higher density fraction exiting through one outlet will contain relatively little of such contaminants. The lighter fraction of the stock containing the majority of the contaminants is either discarded or sent to a further cleaning operation. More commonly, the contaminants to be separated are of higher density than the stock itself so that the higher density fraction contains most of the contaminants and the lower density fraction is relatively contaminant-free. The terms "accept" and "accepted stock", as used in this disclosure, refer to the relatively contaminant-free portion of the stock, and the terms "reject" and "rejected stock" refer to the more contaminated portion of the stock.
Because individual hydrocyclones are ordinarily limited in size and flow capacity, batteries or assemblies including hundreds of individual hydrocyclones are utilized to process stock at the tremendous rates required by modern, high speed industrial operations. For example, apparatus for cleaning paper-making stock at the rate of thirty thousand gallons per minute may include 200 individual hydrocyclones, all connected to a common source of feed stock and all discharging in parallel to common receivers for accepted stock and rejected stock.
The mounting and connection of the numerous individual hydrocylones in such apparatus have posed significant problems. The efficiency of each hydrocyclone in separating the desirable and undesirable fractions of the stock may be affected by fluctuations in the flow of feed stock and by fluctuations in pressure or vacuum conditions at the outlets of the hydrocyclone. Also, the cost of the energy required to pump stock through the apparatus is significant, and complex, flow-restrictive piping arrangements tend to increase this cost. The cost of the initial installation is also a significant problem. Such problem is especially severe in the case of hydrocyclone apparatus for treating stocks, such as paper-making stocks, which are abrasive and corrosive. The fluid-handling elements of such apparatus must ordinarily be fabricated from expensive, difficult-to-work materials such as stainless steel. Accessibility of the individual hydrocyclones for inspection, repair or replacement is also a significant consideration.
The physical orientation of the individual hydrocyclones is also important. The efficiency of some hydrocyclones may be improved if the body of the hydrocyclone is oriented vertically. Thus, in those cases where the lighter fraction of the stock is the accept or desired fraction, the accept outlet of each hydrocyclone should be at the top and the reject outlet at the bottom so that gravity aids in separating the heavy contaminants from the accepted stock. Such vertical orientation of the hydrocyclones is particularly desirable where the apparatus combines the cleaning action of the hydrocyclones with deaeration. In such apparatus, the accept outlets of the individual hydrocyclones may be connected to individual spray pipes extending upwardly into a common accept receiver or plenum which is maintained under vacuum. Accepted stock exiting from the accept outlet or each hydrocyclone sprays upwardly into the plenum, forming relatively finely divided streams or droplets, thus intimately exposing the stock to the vacuum in the plenum to facilitate removal of air contained in the stock.
Compactness of the apparatus is also an important consideration in mounting the apparatus within the mill and in shipping the apparatus to the mill for installation. The need for compactness is especially acute in apparatus employing a vacuum plenum as the receiver for accepted stock. The collapsing forces on such an evacuated plenum imposed by the atmospheric pressure surrounding it increase markedly as the size of the plenum increases. Moreover, such apparatus is often mounted high above the factory floor so that the accepted stock may flow by gravity from the accept plenum to the equipment where it is utilized. This arrangement often necessitates placing the hydrocyclone apparatus adjacent the roof of the factory building, in the limited space available between the roof supporting trusses or columns of the building. Further, the size of any hydrocyclone apparatus mounted at an elevated location should be minimized to minimize the weight of the apparatus and the weight of stock contained in the apparatus and thus minimize the cost of the supporting structure.
One form of multiple hydrocyclone apparatus which has been developed to meet these requirements is described in co-pending, commonly assigned United States patent application Ser. No. 021,623, filed Mar. 19, 1979. As described in said application, the hydrocyclones may be mounted in side-by-side vertical orientation, with their accept outlets at the top and their reject outlets at the bottom. The hydrocyclones are disposed in concentric circular arrays. One or more pipes or conduits extend upwardly adjacent the center of the hydrocyclone arrays to an accept manifold or receiver, mounted above the hydrocyclones. The accept manifold or receiver may be in the form of a unitary cylindrical plenum. A reject receiver or manifold, which also may be in the form of a unitary plenum, may be mounted beneath the hydrocyclones and a feed manifold may be provided adjacent the accept manifold, near the top of the hydrocyclones. The central pipes or conduits serve both as fluid connecting elements and as structural supports for the accept manifold. Moreover, continuations of the centrally disposed conduits extending downwardly below the reject receiver may serve as pedestal supports for the entire apparatus. Each hydrocyclone may be provided with a sight glass at its reject outlet so that the flow from each may be observed and the need for servicing detected by such observation.
This arrangement satisfies the aforementioned requirements to a substantial degree. However, there is still a need for even further improvement in several respects.
The inner hydrocyclones are surrounded by the reject manifold beneath them, the accept manifold or plenum on top of them and the outer arrays of hydrocyclones alongside them. It is therefore difficult to inspect the sight glasses associated with the inner hydrocyclones. It is also difficult to remove or repair any of the inner hydrocyclones without first removing some of the hydrocyclones in the outer arrays. Also, the round shape of the apparatus according to said application creates certain difficulties when especially large numbers of hydrocyclones are to be utilized. As the diameter of the apparatus, i.e., the diameter of the accept receiver or plenum, is directly related to the number of hydrocyclones in the apparatus, apparatus incorporating especially large numbers of conventionally-sized hydrocyclones (more than about 200) requires a receiver or plenum diameter in excess of 12 feet. Such large-diameter receivers may not fit within the spaces commonly provided between roof trusses or columns in factory buildings. Also, they cannot conveniently be transported by truck or railroad.